Thames Water has recently created a publicly accessible web portal which publishes real-time information on when sewage treatment works within the Thames Water network are discharging raw (untreated) sewage to watercourses. This live map has brought the ongoing issue of sewage in our rivers back to public attention. The map can be accessed by anyone here. Although publication of such data will become a legal requirement in coming years, Thames Water’s launching of the portal ahead of it being mandated is a welcome step towards transparency around its operations. Due to the nature of how this data is collected, using Event Duration Monitoring (EDM) which measures start and end time of spills, volume and composition is not recorded and inaccuracies are not uncommon. You can read more about EDM and its limitations here. Despite these limitations, the live data does highlight the unacceptable scale of the problem of raw sewage discharge to watercourses.
Raw sewage spills occur particularly when rainfall infiltrates the sewage network, producing large volumes of dilute sewage, above the volumes that sewage treatment works (STWs) are designed to treat. Many STWs incorporate storage tanks which store excess inflowing raw sewage until it can be treated, thus reducing the extent to which the untreated sewage “spills” into watercourses. However, this is often inadequate to prevent spillage. There is an acceptance that some degree of spillage is inevitable (after heavy, intense rainfall). However, RTCT and many others believe raw sewage spills into rivers happen too often, and sometimes in circumstances where rainfall is less than extreme.
RTCT recognises that the contributory factors are complex. Thus, whilst we have concerns over STW capacity lagging behind demand from wastewater inputs, a key cause of raw sewage spillage is too much clean rain and groundwater making its way into the sewage network, and then on to STWs. Again, this is in part a consequence of a legacy of underinvestment in sewage networks (leaky sewage pipes enabling groundwater to infiltrate) but also increased urbanisation, resulting in more rain runoff going directly to the sewage network. Recognising the need to prevent problems caused by large volumes of clean water entering the sewage system, Thames Water recently published its Drainage and Surface Water Management Plan (DWMP). RTCT and the River Thame Catchment Partnership, which we co-host, welcome the DWMP approach, albeit we have concerns about the ambition and timescales of the DWMP in addressing the frequency and duration of raw sewage discharges from STWs. The Catchment Partnership’s response to TW’s DWMP can be found here.
It’s worth distinguishing the issue of raw sewage spills from the overall performance of STWs under normal conditions – which is also a key issue of concern for RTCT. General poor water quality is a feature of the River Thame, with none of its tributaries attaining “good ecological status”. Whilst poor water quality is not solely caused by STWs, but also agricultural and urban runoff, monitoring and modelling led by UKCEH with RTCT shows a strong “signature” of sewage treatment effluent (treated) versus other sources. These results are supported by our growing body of evidence gathered by our new Water Quality Monitoring Network, an initiative where volunteers trained by RTCT are monitoring 40 strategically selected sites across the catchment every month. From anecdotes from concerned locals to citizen science data to rigorous scientific analysis, the evidence points to a chronic issue of unnaturally high nutrient levels in the catchment. And this issue isn’t new, pollution from sewage was a key driving factor behind the formation of RTCT and to this day we continue to push for change that will bring improvements to water quality & benefit wildlife and river users. We hope the accessible and visible nature of Thames Water storm overflow data will energise others to join our efforts to push for investment in sewage treatment capacity and improved infrastructure. We will continue our multi-faceted approach to advocating for tangible improvements.
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